Thinset Calculator
How many 50-lb bags of thinset your tile job takes — coverage depends mostly on trowel notch size, so that is the main input.
Result
| Bags before rounding |
Units & conversions used
Area is in ft² (metric inputs convert at 1 m² = 10.7639 ft²). Bags are the standard US 50-lb bag of dry thinset mortar; coverage per bag always refers to that bag size.
Formula & source
Source: coverage per bag comes from the trowel/coverage charts manufacturers publish for each mortar. Commonly published chart ranges for a 50-lb bag are roughly 90–110 ft² for a 3/16 in V-notch, 75–85 ft² for a 1/4 × 1/4 in square-notch, and 35–45 ft² for a 1/2 × 1/2 in square-notch; this calculator uses the mid-points (100 / 80 / 40). Your product's chart governs — check the bag.
Worked example (you can verify by hand)
Input: 200 ft² of tile set with a 1/4 in square-notch trowel (80 ft² per bag).
- Bags before rounding: 200 ÷ 80 = 2.5
- Round up — thinset is only sold by the full bag
Expected output: 3 × 50-lb bags.
Limitations — what this cannot do
- Coverage varies with substrate flatness, trowel angle and technique, and the tile's back profile — deeply keyed tile backs use more mortar than smooth ones.
- Back-buttering large-format tile (recommended for tiles with any side 15 in or longer) adds a second layer of consumption this estimate does not include; order an extra bag on large-format jobs.
- It covers the setting bed only — leveling compounds, waterproofing membranes, crack-isolation products and grout are separate materials.
- Do not re-temper (re-mix with added water) thinset that has stiffened in the bucket; plan batches around the product's pot life instead of stretching a mix.
FAQ
Which trowel do I use for 12×12 tile?
A 1/4 × 1/4 in square-notch is the common starting point for tile up to about 12 in. Large-format tile (any side 15 in or longer) typically needs a 1/2 × 1/2 in notch plus back-buttering to reach the 80–95% mortar coverage standards call for in dry areas (more in wet areas).
Modified or unmodified thinset — what's the difference?
Modified thinset contains polymers for bond strength and flexibility and suits most floors and porcelain tile. Unmodified is required in specific assemblies — notably between certain waterproofing membranes and tile — where the membrane maker specifies it. The membrane and tile manufacturers' instructions govern.
How much does thinset cost?
A 50-lb bag of standard polymer-modified thinset commonly sells in the $15–$35 range (2025–2026); premium large-and-heavy-tile (LHT) mortars commonly run higher. Mortar is a modest line item next to tile itself, but running out mid-job while a bed is open is a real problem — rounding up a bag is cheap insurance.
How long do I have to work with a mixed batch?
Typical pot life is 2–3 hours depending on product and temperature (check the bag). Mix half a bag at a time on big floors, keep the bucket shaded, and discard mortar that has started to set — re-wetting it destroys bond strength.